(1) Field of the Invention
The present invention relates to a developing unit for use in an image forming apparatus such as a laser printer, copier, facsimile machine etc., and in particular relates to a technology for replenishing, as required, the toner for image development to the developer hopper as a part of a developing unit.
(2) Description of the Prior Art
An image forming apparatus such as a laser printer, copier, facsimile machine utilizing the electrophotographic technique, has an image forming portion for forming a desired image on a sheet for recording. In this image forming portion, the surface of a photoreceptor as an image bearer is uniformly electrified with charge of a particular polarity and then is illuminated with an optical image so as to form a static latent image corresponding to the image. For the purpose of visualizing this static latent image, the image forming portion includes a developing unit and other components. The developing unit is configured of a developer hopper holding a developer and having a developing roller for replenishing the developer to the developing position where the developing roller opposes the photoreceptor. Further, since the toner in the developer hopper is consumed, a toner replenishing device for supplying the toner to the developer hopper as necessary is arranged adjacent to the developer hopper.
In a developing unit of the above type, if the toner reserve container for replenishing the developer to the developer hopper is arranged on the top, the developing unit would be bulky as to its height so a waste space would arise inside the image forming apparatus, thus making the whole image forming apparatus bulky. For this reason, the toner reserve container is horizontally arranged adjacent to the developer hopper to reduce the height of the developing unit, thus making the developing unit into a thinned configuration and hence making it possible to configure a compact image forming apparatus as a whole by eliminating the unnecessary space which would arise inside the image forming apparatus.
An example of such a developing unit is disclosed in Japanese Patent Application Laid-Open Sho No. 63-213877. In this developing unit, the toner reserve container is arranged at the side of the developing hopper and has a conveying element that conveys and agitates the toner inside the toner reserve container so that the conveying element feeds (replenishes) the toner into the toner replenishing portion from which the toner is replenished to the developer hopper.
Japanese Patent Application Laid-Open Hei No. 10-123815 has proposed a developing unit having a toner replenishing device having a simpler configuration compared to the developing unit disclosed in the aforementioned publication. This developing unit 60 comprises, as shown in FIG. 1, a developer hopper 61 which incorporates an agitating roller 62 for agitating the developer stored in developer hopper 61 and a developing roller 63 for conveying the developer to the developing area that opposes the photoreceptor. Further, a toner reserve container 64 is horizontally arranged at the side of developer hopper 61. Toner reserve container 64 stores toner 69 for replenishment and incorporates an agitator 65 that agitates and conveys the stored toner 69.
Formed between developer hopper 61 and toner reserve container 64 is a toner supply opening 66, at which a toner replenishing roller 67 made up of sponge for replenishing the toner into developer hopper 61 is positioned. The agitator 65 is rotated in the direction of the arrow in the drawing during toner replenishment so as to feed the toner to replenishing roller 67 whilst agitating the toner stored in toner reserve container 64.
Agitator 65 is configured of rotational, agitating vanes (a pair of plates arranged on both sides) with a conveying sheet 68 of a flexible sheet-like element, attached atone end of the vanes. Accordingly, as agitator 65 is turned, conveyer sheet 68 scoops up the toner 69 accumulated or stored at the bottom of toner reserve container 64 whilst agitating it and collects the toner thereover to feed it to replenishing roller 67. During this, the toner 69 covering the sheet is supplied to replenishing roller 67 by making use of the force of action that causes conveying sheet 68 to restore itself due to its own flexibility.
In a developing unit of this kind, toner reserve container 64 is arranged at the side, and the agitator 65 is provided in the toner reserve container 64, whereby toner 69 in toner reserve container 64 can be conveyed completely to toner replenishing roller 67. Thus, the toner storage volume can be increased by enlarging the developing unit horizontally while the height of the developing unit can be suppressed.
In the developing unit shown in FIG. 1, since toner reserve container 64 is horizontally arranged at the side of developer hopper 61, there is no increase in height. However, if the toner storage volume of toner reserve container 64 is further increased, the height cannot but increase.
If toner reserve container 64 is enlarged only in the horizontal direction in order to increase the toner storage volume, agitator 65 shown in FIG. 1 cannot agitate and convey the toner well enough. That is, if the distance of conveying sheet 68 from the fixed end to the distal end is set long enough to convey the toner in the vertical direction, it is difficult to secure good enough performances of agitation and conveyance of the toner in the lateral direction. As a result, the toner inside toner reserve container 64 cannot be completely used and a certain toner will remain unused. Further, the remaining toner is not agitated and hence the toner gathers into a mass in the stationary area, which may then be fed into the agitatable area by some reason such as vibration, for instance, and hence the aggregation may be fed to replenishing roller 67. When such a toner aggregation is fed to developer hopper 61, it may cause development failures, or other deficiencies.
For these reasons, in the apparatus disclosed in Japanese Patent Application Laid-Open Hei No. 10-123815, the rotary shaft 65a of agitator 65 is set off-centered closer to the developer hopper 61 side while conveying sheet 68 when it is positioned horizontally is formed long enough so that its front end reaches the right side wall (rear wall) of toner reserve container 64 in FIG. 1, whereby toner supply can be stabilized while securing a desired amount of toner for replenishment and eliminating toner stagnation. In FIG. 1, a reference numeral 71 designates a regulating element for limiting the developer adhering to developing roller 63 to the predetermined amount and 72 designates a concentration detector for detecting the toner concentration of the developer in developer hopper 61.
Here, in accordance with the toner replenishing device having a configuration shown in FIG. 1, toner 69 in toner reserve container 64 is adapted to be scooped up and fed to the replenishing portion from above to replenishing roller 67. In contrast to this, those disclosed in Japanese Patent Application Laid-Open Hei No. 6-236110 and Japanese Patent Application Laid-Open Hei No. 7-271163 are configured so that the toner in the toner reserve container is scooped up and fed from below. In these cases where the toner is fed in such a manner, the rotary shaft of the agitator needs to be positioned above the replenishing portion so that the configuration inevitably tends to be greater in height.
Here, the developing unit having a configuration shown in FIG. 1, particularly, agitator 65 rotatably provided in toner reserve container 64 for toner replenishment is configured to be symmetrical with respect to rotary shaft 65a. In other words, agitator 65 is set so that the distance from the center of rotary shaft 65 to either end is constant, and conveying sheet 68 is attached to one of the ends.
Therefore, when agitator 65 is set vertically as shown in FIG. 1, conveying sheet 68 is positioned horizontally and comes closer to a top openable/closable lid 70 of toner reserve container 64. In other words, the distance between openable/closable lid 70 and conveying sheet 68 is very short. Hence, when agitator 65 is turned in the direction shown in the drawing, a mid part of conveying sheet 68 comes into contact with the openable/closable lid 70, whereby the scooped toner falls out of the distal end of conveying sheet 68 and hence it becomes difficult to feed a sufficient enough amount of toner to the position of replenishing roller 67. Further, conveying sheet 68 is deformed excessively so that a large amount of toner spills from the retaining sheet.
Besides, as shown in the drawing, the distal part of conveying sheet 68 is formed with a flexed portion 68a (bent with an angle xcex8) so as to scoop up the toner adequately. This configuration is to secure a sufficient amount of toner to be supplied to toner replenishing roller 67. However, even with this configuration, when agitator 65 is turned, a mid portion, in place of the distal end, of conveying sheet 68 may come first into contact with top openable/closable lid 70 as described above, or conveying sheet 68 may be deformed excessively, so that a large amount of the toner scooped up by flexed portion 68a at the distal end of the sheet will conceivably fall out.
Further, when conveying sheet 68 is turned by agitator 65 to scoop up the toner and supply the toner while being in contact with openable/closable lid (top plate) 70, the sheet is greatly deformed and curved by the contact. In this case, if the sheet is greatly curved and flexed but the flexure is not uniform across the full length of the rotational axis (in the longitudinal direction), the supplied amount of the toner to replenishing roller 67 will vary and fluctuate. Specifically, if the flexure of conveying sheet 68 is irregular along the rotational axis of replenishing roller 67, the supplied amount of the toner across the length in the axial direction will not be uniform, presenting local deficiencies of toner. For this reason, the toner supplied to the developer hopper 61 side by replenishing roller 67 greatly varies across the length in the rotational axis direction, which in turn, appears as image unevenness due to fluctuations of toner concentration.
In view of the above problems, it is an object of the present invention to provide a developing unit equipped with a toner replenishing device wherein the toner in the toner reserve container can be sufficiently fed and conveyed to the toner replenishing portion with an improved efficiency.
It is another object of the invention to eliminate partial toner supply and hence local fluctuations of the development density so as to realize development with substantially uniform density as a whole, in particular, across the length in the axial direction.
It is a further object of the invention to provide a developing unit which is simplified in its structure in order to realize sufficient replenishment of the toner to the toner replenishing portion.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a developing unit equipped with a toner replenishing device having a toner reserve container for replenishing the toner to a developer hopper as required and a replenishing portion for supplying the toner stored in the toner reserve container to the developer hopper, includes:
a rotator incorporated in the toner reserve container so as to be rotatable for agitating the stored toner; and
a conveying sheet of a flexible material arranged so as to become closer to the rotary shaft of the rotator, for scooping up the stored toner and conveying it to the replenishing portion.
In accordance with the second aspect of the present invention, a developing unit equipped with a toner replenishing device having a toner reserve container for replenishing the toner to a developer hopper as required and a replenishing portion for supplying the toner stored in the toner reserve container to the developer hopper, includes:
a rotator incorporated in the toner reserve container so as to be rotatable for agitating the stored toner; and
a conveying sheet of a flexible material attached to the rotator for scooping up the stored toner and conveying it to the replenishing portion, and is characterized in that the top plate of the toner reserve container with which the distal end of the conveying sheet comes in contact is provided with a recessed portion, projected portion or rough-faced portion made up of one or multiple sections or any combination of these so as to briefly grip the distal end of the conveying sheet.
In accordance with the third aspect of the present invention, the developing unit equipped with a toner replenishing device having the above first feature is characterized in that the top plate constituting the upper part of the toner reserve container has a portion inclined or curved toward the replenishing portion so as to prevent the conveying sheet from abruptly springing back from its flexed state to its original shape when the conveying sheet feeds the toner to the replenishing portion as its distal end abuts against and slides along the top plate and allows the conveying sheet to gradually restore itself.
In accordance with the fourth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above second feature is characterized in that the top plate constituting the upper part of the toner reserve container has a portion inclined or curved toward the replenishing portion so as to prevent the conveying sheet from abruptly springing back from its flexed state to its original shape when the conveying sheet feeds the toner to the replenishing portion as its distal end abuts against and slides along the top plate and allows the conveying sheet to gradually restore itself.
In accordance with the fifth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above third feature is characterized in that the inclined or curved portion formed in the top plate originates from the point where the conveying sheet starts reverting itself to its original shape from its maximally flexed state.
In accordance with the sixth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above fourth feature is characterized in that the inclined or curved portion formed in the top plate originates from the point where the conveying sheet starts reverting itself to its original shape from its maximally flexed state.
In accordance with the seventh aspect of the present invention, the developing unit equipped with a toner replenishing device having the above third feature is characterized in that the inclined or curved portion of the top plate is angled with an angle xcex81 which is equal to or smaller than 15 degrees.
In accordance with the eighth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above fourth feature is characterized in that the inclined or curved portion of the top plate is angled with an angle xcex81 which is equal to or smaller than 15 degrees.
In accordance with the ninth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above first feature is characterized in that the conveying sheet is formed with such a length that its distal end is placed in proximity to the rear wall of the toner reserve container when the conveying sheet is positioned in parallel to the top plate of toner reserve container and the distal end part is flexed at an angle xcex8 to form a toner retainer.
In accordance with the tenth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above second feature is characterized in that the conveying sheet is formed with such a length that its distal end is placed in proximity to the rear wall of the toner reserve container when the conveying sheet is positioned in parallel to the top plate of toner reserve container and the distal end part is flexed at an angle xcex8 to form a toner retainer.
In accordance with the eleventh aspect of the present invention, the developing unit equipped with a toner replenishing device having the above second feature is characterized in that the recessed, projected or rough-faced portion formed on the top plate constituting the toner reserve container is formed of multiple sections arranged one behind another with respect to the rotational direction of the conveying sheet, and the recessed, projected or rough-faced section on the downstream side provides a stronger grip than that on the upstream side.
In accordance with the twelfth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above second feature is characterized in that the recessed, projected or rough-faced portion formed on the top plate constituting the toner reserve container is formed close to the replenishing portion.
In accordance with the thirteenth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above second feature is characterized in that the conveying sheet is attached at its one end in proximity to the rotary shaft of the rotator.
In accordance with the fourteenth aspect of the present invention, the developing unit equipped with a toner replenishing device having the above second feature is characterized in that the rough-faced portion formed on the top plate constituting the toner reserve container is specified so that the mean roughness (Ra) is set within the range of 5 to 500 xcexcm and the maximum roughness (Rmax) is set within the range of 15 to 1500 xcexcm.
The features of the invention are as above, and the operational effects produced by the above features of the invention will be described hereinbelow.
First, by the configuration of the above first feature, the toner stored in the toner reserve container is fed (conveyed) by the conveying sheet to the toner replenishing portion as the rotator turns. During this, with its distal end abutting against the top plate forming the upper part of the toner reserve container, the conveying sheet is being deformed and largely flexed and moves along the top plate, retaining and conveying the toner to the replenishing portion. Since the conveying sheet is attached to a certain point so that it comes closer to the rotary shaft of the rotator, it is possible to secure a distance from the top plate and hence avoid the sheet being excessively flexed by the top plate. Therefore, it is possible to prevent the toner retained on the sheet from locally spilling out and hence prevent local degradation of conveyance of the toner. Accordingly, conveyance of feeding the toner in the toner reserve container to the replenishing portion can be enhanced, in particular, the toner can be conveyed practically uniform across the full range of the rotary shaft. Resultantly, the amount of the toner supplied to the developer hopper as a part of the developing unit can be made substantially uniform across the full length in the axial direction, thus making it possible to beneficially keep the developing density without causing any local variations in developing density.
In accordance with the configuration of the second feature, with the rotation of the rotator, the conveying sheet turns and scoops up the stored toner. When the sheet comes in contact with the top plate, it becomes curved and flexed. As the sheet is bent more, the sheet will not be flexed uniformly across the length along the rotary shaft and local irregularities of the bending state tend to be stronger. In this state, when the distal end of the conveying sheet is caught by the recessed portion, projected portion or rough-faced portion, local irregularities of the bending state of the sheet can be corrected so as to be uniform. In this way, the bending state is made uniform so that the toner scooped and retained by the conveying sheet can be uniformly supplied to the replenishing portion across the full range along the axial direction, thus making the distribution of toner concentration in the developing unit after toner replenishment uniform. This leads to uniform toner density after development. Here, use of the recessed portion, projected portion or rough-faced portion made up of multiple sections or combination of these is effective in reliably and efficiently uniformly correct the bending state of the conveying sheet.
By the provision of the configurations defined by the third and fourth features, the conveying sheet that comes in contact with the top plate and hence is deformed, can be prevented from flicking the toner excessively by its repulsive force and degrading its conveyance capability when the sheet reverts itself back to its original shape while the conveying sheet feeds the retained toner to the replenishing portion. Therefore, occurrence of local conveyance failures can be avoided to thereby enable a more stable conveyance. That is, the configuration of the top plate inclined or curved toward the replenishing portion can reduce the strong repulsive force when the conveying sheet restores to its original state and enables beneficial conveyance of the toner retained by the conveying sheet to the replenishing portion.
Next, in accordance with the configurations of the fifth and sixth features, the inclined or curved portion formed in the top plate originates from the point where the conveying sheet starts reverting itself to its original shape from its maximally flexed state. Therefore, this configuration makes it possible to reduce the strong repulsive force when the conveying sheet restores to its original state and hence promote the effect of improving the conveying performance, improving the conveying performance of the toner to the replenishing portion, thus further stabilizing toner replenishment to the developer hopper.
In accordance with the configurations of the seventh and eighth features, the inclined or curved portion of the top plate is angled with an angle xcex81 which is equal to or smaller than 15 degrees. In this case, if the angle xcex81 exceeds 15 degrees, the conveying sheet may be deformed excessively and hence the retained toner would locally spill out, causing local irregularities in toner conveyance to the replenishing portion. In this configuration, setting of the angle xcex81 equal to or smaller than the 15 degrees enables beneficial retaining of the toner and maintains stable conveyance of the toner.
By the provision of the configurations defined by the ninth and tenth features, the toner stored in the toner reserve container can be fully agitated by the conveying sheet and almost all the toner can be conveyed to the replenishing portion. Further, positioning of the rotator or the rotary shaft off the center to the developer hopper side facilitates beneficial agitation and conveyance of the stored toner even if the toner reserve container is formed so that its horizontal dimension is elongated. Further, since the distal end of the conveying sheet is flexed at an angle xe2x96xa1, it is possible to realize a further enhanced toner retaining state and stabilized conveyance.
In accordance with the configuration of the eleventh feature, the bending state of the conveying sheet can be corrected uniformly, and then the distal end of the sheet is gripped by the final, large recessed, projected or rough-faced portion so as to adequately bend the sheet retaining the toner thereon when it replenishes the toner to the replenishing portion. Therefore, it is possible to flick the toner by this elastic action of the flexure, realizing a stable replenishment as well as an ample amount of toner supply.
Next, according to the configuration of the twelfth feature, it is possible to reform the bending state of the conveying sheet being curved near the replenishing portion uniformly. Therefore, it is possible to realize stable toner supply and uniform toner replenishment across the full range in the axial direction.
According to the configuration of the thirteenth feature, since the bending amount of the conveying sheet can be reduced, it is possible to further stabilize the bending state while improving the toner retaining capacity. In combination with this effect, the bending state can be corrected by the recessed or projected portion. Therefore, it is possible to further enhance stable toner supply, uniformity of the replenished amount, in particular uniformity of the replenished amount across the full range in the axial direction.
Finally, setting of the surface roughness according to the fourteenth feature, further enhances the reliability of gripping the conveying sheet. Further, the sheet can be smoothly regulated instead of being abruptly stopped, thus making it possible to avoid the scooped toner held by the conveying sheet from falling and hence realize a further stabilized toner feeding.